Calculate radius, diameter, circumference, or area of a circle – enter any one value.

Circle Diagram

Enter Value

Radius (R)

Diameter (D)

Circumference (C)

Area (A)

Circle Knowledge Quiz

Test your understanding of circles with these real-world scenario questions. Select an answer and submit to see if you're correct!

About Circles

A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the center. The distance between any point of the circle and the center is called the radius.

Circle Formulas

Diameter

D = 2R (Diameter is twice the radius)

Circumference

C = 2πR or C = πD (Distance around the circle)

Area

A = πR² (Space inside the circle)

Pi (π)

π ≈ 3.14159 (Mathematical constant)

Real-world Examples

Pizza: The size of a pizza is usually measured by its diameter
Wheels: The circumference determines how far a wheel travels in one rotation
Clocks: Clock faces are circular, with the radius determining the size
Planets: Planets and celestial bodies are approximately spherical
Coins: Most coins are circular in shape

Tips for Using the Circle Calculator

Enter Only One Value

Our calculator requires you to enter only one value (radius, diameter, circumference, or area). The other values will be calculated automatically.

Use Consistent Units

Make sure to use consistent units for all measurements. The calculator will maintain the same units for all results.

Check Your Results

Always double-check your results, especially for important calculations. Our calculator provides step-by-step explanations to help you understand the process.

Learn the Formulas

Understanding the formulas behind the calculations can help you solve circle-related problems even without a calculator.

Frequently Asked Questions

What is the difference between circumference and diameter?

The diameter is the distance across the circle through its center, while the circumference is the distance around the circle. The circumference is approximately 3.14 times the diameter.

What units can I use with this calculator?

You can use any consistent units (mm, cm, m, km, in, ft, yd, mi). The calculator will maintain the same units for all results.

How accurate are the calculations?

Our calculator uses the value of π (pi) to high precision, ensuring accurate results. However, rounding may occur in the display of results.

Can I calculate the area of a circle if I only know the circumference?

Yes, you can. Enter the circumference value, and the calculator will determine the radius and then calculate the area using the formula A = πR².

What is the value of π (pi) used in this calculator?

This calculator uses a high-precision value of π (pi) for accurate calculations. π is an irrational number approximately equal to 3.14159.

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